Motor powered or wind powered movement of boats is greatly impeded by friction or drag arising from the contact of the moving hull with adjacent water. Friction can be reduced to some extent by configuring the hull with hydrodynamic principles in mind but this may adversely affect other characteristics of the boat. For example, flattening of the hull reduces drag by reducing the area of the hull that is in contact with water but also roughens the travel of the boat particularly in the the presence of waves.
Certain prior forms of watercraft reduce frictional drag by creating and entrapping a cushion of air beneath the hull or at least a portion of the hull. Confining the air cushion requires that there be a sizable concavity in the underside of the hull or that skirts extend downward from the hull along the boundaries of the air cushion. The rim of the concavity or the lower edges of the skirts must lie in a horizontal plane in order to entrap the air cushion and thus the technique mandates an essentially flat bottomed hull configuration. Thus these prior air cushions are not applicable to all forms of hull configuration and are generally limited to small craft of the type that plane along the water surface when traveling at high speed.
Air cushioning is carried to an extreme in a class of watercraft known as surface effect ships or hovercraft. Such vessels have a skirt encircling the underside of the craft and are supported above the water during operation by forcing a downflow of air into the region encircled by the skirt. This again dictates that the craft have an essentially flat and horizontal underside. Reduction of friction is gained at the cost of substantially increased power requirements and a loss of precision in controlling movement of the craft.
It would be advantageous if friction resistance to movement of a boat could be reduced without introducing constraints on the configuration of the boat hull. This would increase the efficiency of boats having, for example, V-shaped hulls or U-shaped hulls without compromising the operational advantages of such hulls such as stability, passenger comfort, cargo capacity and manuverability.
Frictional resistance to the motion of boats and ships is also increased by barnacles which adhere to the hull. Coating of the hull with barnacle repelling paints or the like is only temporarily effective and can cause environmental problems by releasing harmful constituents of the paints into the water.
The present invention is directed to overcoming one or more of the problems discussed above.